Reduced forms of Cyanocobalamin, with a Co(I) (top), Co(II) (middle), and Co(III) (bottom)
In the cobalamins, cobalt normally exists in the trivalent state, Co(III). However, under reducing conditions, the cobalt center is reduced to Co(II) or even Co(I), which are usually denoted as B 12r and B 12s, for reduced and super reduced, respectively.
